When most people hear the word "nematode" they think of the common root knot nematode that works beneath the soil line. However, an increasingly common pest in the landscape are nematodes that feed in the foliage.

Generally, they belong to the genus, Aphelenchoides, which infest about 200 host plants. Some of the most common hosts include Japanese anemone, begonia, chrysanthemum, strawberry, hosta, iris, phlox, verbena, zinnia, dianthus, impatiens, ferns, trillium and African violet.

Symptoms: By far, the most common sign of the presence of foliar nematodes is the browning of the area between the leaf veins later in the growing season. The damage starts with linear striping along the veins. Later, these areas turn to a water soaked appearance eventually turning to dead, brown tissue.

More difficult to detect signs would be a lack of vigor in the plant, lack of flowering, stunting and, rarely, death of the plant. Newly emerged, late season leaves may appear symptom free.

Life Cycle: Foliar nematodes generally overwinter in the crown of the plant, on dormant buds or, sometimes, on leftover debris. The nematodes can swim around the plant or from plant to plant on surface water. They are spread in splashing water, from plant leaves in contact with each other or through contact with pruning tools and during propagation.

Managing Foliar Nematodes: Foliar nematodes are not easy to control or eliminate once they are in the garden. However, certain preventative steps may help to manage the problem.

  • Sanitation - If you find foliar nematodes in your garden, remove the infested plants and dispose of them away from the garden. Do not put them in the compost pile! Also, if you have the problem, take care to sterilize pruners and other equipment used on the infested plants. You can use a one part bleach to nine part water solution.

    Some people have had success using heat to eliminate foliar nematodes from especially valuable plants. This involves placing the dormant crowns in water at 120 degrees F for 15 minutes. If the water is too hot, it may damage or kill the plant. If it is not warm enough, it will be ineffective.

  • Use Disease Free Plants - Nurseries that sell plants such as Hostas that are known to host nematodes should be careful to sell only nematode free plants. Also, take care in accepting gift plants or buying plants at a neighborhood sale that have not been inspected for nematodes.

  • Resistance - It appears that some cultivars of chyrsanthemums are resistant to foliar nematodes. Unfortunately, such resistance has not yet been found in other susceptible host species.

  • Pesticides - At this time, the handful of nematicides that are effective in treating foliar nematodes are only available to licensed, commercial applicators. There are currently no nematicides labeled for home use against foliar nematodes.

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.

 

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